Handover is the process of automatically transferring a connection in progress between a mobile device and one cell of a mobile communication environment to another cell as a consequence of the mobility of the mobile device or, in other words, as a consequence of user movements. This process generally requires some detection of the necessity of the handover and then the switching of the transaction from a cell of the mobile communication environment to another cell while keeping user disturbance to a minimum.
In the following, without imposing a restriction on the type of mobile communication environment—i.e., cellular mobile telephone network, wireless LAN, PDC—it is assumed that the coverage area of the mobile communication environment divides into a plurality of cells. It is also assumed that communication between a mobile device located in the mobile communication environment, in particular a specific cell thereof, and the mobile communication environment is supported through at least one access point in each cell.
Typically, the mobile device will traverse different cells in the mobile communication environment when roaming therein. Here, the problem is to decide which access point to choose. State of the art are many algorithms based on signal strength analysis or on available radio resources in view of a location of the mobile device and surrounding access points. Even if one access point is slightly better regarding these local measurements, the decision may not be the best. E.g., one might consider a situation where a mobile device is located in a train. In such a case it is obviously better to hand over to an access point situated nearly to the train track, even if another access point is better reachable for a short period of time.
Therefore, in may cases the handover can be optimized by considering the mobile device movement and user preferences. E.g., if the mobile device is located in a car or train, its route may be constrained to certain cells and related access points in the mobile communication environment. Further, the mobile device profile may contain information that the mobile device is built into a car. Alternatively, the movement pattern of the mobile device suggests that the user is travelling in a train.
However, a main problem not considered so far in the state of the art is that handover decisions have to be executed fast. Nevertheless, the mobile device profile and location information is only available on a central server in the mobile communication environment. Therefore, retrieving this information may be too slow for achieving optimal handover decisions. Even worse, in some cases the radio conditions during handover may be so poor that they even prohibit exchange of such information.